A recent development in the optical transmission field has been the introduction of amplified systems. These systems dispense with the convention digital repeaters or regenerators, commonly referred to as "3R repeaters", and instead provide direct amplifications of the transmitted signal. This can result in a significant cost reduction as the expensive 3R repeaters of a conventional system can be replaced by relatively low cost amplifiers. Typically an amplified system comprises an optical fibre path along which optical amplifiers are disposed at regular intervals. These amplifiers may comprise erbium amplifiers.
A problem associated with the introduction of amplified systems has been the lack of a suitable supervisory system to provide remote monitoring of the performance of each system amplifier. It will be appreciated that, in an amplifier system where there is no retiming or reshaping of the transmitted signal, poor performance of a single amplifier can seriously impair the operation of the system. The successful commercial operation of such a system cannot therefore be achieved without an adequate supervisory system.
The object of the invention is to minimise or to overcome this disadvantage.